[Peaker]

The content of Fun is actually the type: Context -> Value -> (Context, Value).

If you flip the arguments, you get: Value -> Context -> (Context, Value). The (Context -> (Context, Value)) is actually the State type:

    State s a = s -> (s, a)

I modified your code to use this type. During the process, I encountered some peculiar things (and factored out some things), see comments in code.

https://gist.github.com/950445

Funny that it turns out slightly longer when re-using more code due to syntactic artifacts. Monad comprehensions (recently restored to GHC via an extension) would resolve that.

[die_sekte]

The eval throwing away context does not make any sense in retrospect. I think I made it that way because of some ghetto-scoping ideas.

You broke car and cdr somehow (these don't evaluate their arguments anymore), but I have no idea how you did this.

This was mostly a training exercise, this is why there is no significant use of monads in there: I simply haven't learned enough about them to feel comfortable using them.

[Peaker]

Can you give the example that breaks car/cdr? They seem to be evaluating their args here:

    fst $ repl "(car (cons 1 (quote ())))"
    Number 1

[die_sekte]

Sorry, that was my fault. I didn't make lambdas evaluate their arguments and I didn't notice this in my code. I.e. car/cdr work correctly, fun doesn't.